Nancy (McElrath) Dobson, Burke Co., NC

Alexander Dobson (1793-1876) of Burke Co., NC married secondly about 1840 Sarah M. (1806-1895), who is known to her descendants as Sarah McElrath. R.D. Floyd lists her (for reasons unknown) as McElrath/Mitchell. Was she a McElrath, widow of a McElrath, or a Mitchell?Would appreciate any insight.